Ion producing source for electrostatic recording apparatus

ABSTRACT

An electrophotographic film member is disposed in darkness for charging the photoconductive coating thereof so that it may subsequently be exposed to a light pattern for forming an electrostatic latent image of said light pattern on the coating. Means are provided for charging the coating in such a manner that there is a minimum of radiation produced by the charging means, specifically so that ultra violet radiation is minimized. This is accomplished by the use of some form of ultra violet radiation shielding means in association with a corona wire or array of corona wires. Alternatively ionization means such as a high-speed high-voltage spark gap may be utilized. The method of the invention comprises charging the photoconductive coating of the electrophotographic film member in darkness while excluding ultra violet radiation therefrom. A modified method comprises producing ions in a step which, while initially producing ultra violet radiation, discontinues the emission of such radiation a substantial time before the ions recombine to dissipate, and charging the photoconductive coating thereby.

United States Patent 11 1 Kuehnle 1 1 ION PRODUCING SOURCE FORELECTROSTATIC RECORDING APPARATUS [75] Inventor: Manfred R. Kuehnle.Lexington.

Mass.

[73] Assignee: Coulter Information Systems. Inc..

Bedford. Mass.

[22] Filed: Sept. 14. 1973 [21] Appl. No.: 397.307

[52] U.S. Cl 355/3 R: 96/1 C: 250/324:

[51] Int. Cl. G033 15/00 [58] Field of Search 355/3 R: 317/262 A;250/324. 326: 96/1 C [56] References Cited UNITED STATES PATENTS2.543.051 2/1951 Oughton et a1. 317/262 A 2.803.177 8/1957 Lowrie 355/32.993.787 7/1961 Sugarman.... 355/3 X 3.1 17.5(11 1/1964 Oliphant 355/33.411.846 11/1968 Naroff... 355/3 3.557.367 1/1971 Roth 317/262 A3.566.110 2/1971 Gillespie 317/262 A 3.660.656 5/1972 Frank et a1.317/262 A 3.675.096 7/1972 Kicss 317/262 A 1451 Apr. 29, 1975 PrimaryE.\'amincrRichard L. Moses Allurm'y. Agent. or Firm-Silverman & C ass.Ltd.

[57 I ABSTRACT An electrophotographic film member is disposed indarkness for charging the photoconductive coating thereof so that it maysubsequently be exposed to a light pattern for forming an electrostaticlatent image of said light pattern on the coating. Means are providedfor charging the coating in such a manner that there is a minimum ofradiation produced by the charging means. specifically so that ultraviolet radiation is minimized. This is accomplished by the use of someform of ultra violet radiation shielding means in association with acorona wire or array of corona wires. Alternatively ionization meanssuch as a highspeed high-voltage spark gap may be utilized.

The method of the invention comprises charging the photoconducti ecoating of the electrophotographic film member in darkness whileexcluding ultra violet radiation therefrom. A modified method comprisesproducing ions in a step which. while initially producing ultra violetradiation. discontinues the emission of such radiation a substantialtime before the ions recombine to dissipate. and charging thephotoconductive coating thereby.

7 Claims. 11 Drawing Figures ION PRODUCING SOURCE FOR ELECTROSTATICRECORDING APPARATUS CROSS-REFERENCE TO RELATED APPLICATIONS Referencewill be made herein to the electrophotographic film which is disclosedand claimed in a copending application entitled: ELECTROPHOTO- GRAPHICFILM. METHOD OF MAKING AND USING THE SAME AND PHOTOCONDUCTIVE COATINGUSED THEREWITH. Ser. No. 378.l8(l. filed July ll. I973.

Reference will be made herein to a camera construction which isdisclosed andclaimed in a copending application entitled. SHUTTERLESSCAMERA SYS- TEM. Ser. No. 397.309 filed Sept. 14. 1973.

The basic method of and apparatus for utilizing peak potential surfacecharge for adjusting the sensitivity of the electrophotographic film ofthe said copending application Ser. No. 378.180 in a camera constructionare disclosed in two copending applications entitled IMAGE RECORDINGMETHOD FOR ELECTRO- PHOTOGRAPHIC FILM, Ser. No. 389.l49 filed Aug. 17.I973 and "IMAGE RECORDING APPARA- TUS FOR ELECTROPHOTOGRAPHIC FILM".Ser. No. 389.124 filed Aug. 17. 1973. I

All of the above applications as well as the present one are owned bythe same assignee.

BACKGROUND OF THE INVENTION The invention herein is concerned with theart of electrostatic recording and more particularly is concerned with anovel apparatus and method for effecting such recording.

Electrostatic apparatus and techniques which are known at the presenttime are characterized by the relatively slow speed with which themethod is carried out and the apparatus is used. The basic member. whichis called an electrophotographic member herein for certain reasons whichwill appear. is a layer of photoconductive material based upon a supportthat includes at least a conductive member. In the xerographic processas known, the photoconductive layer is amorphous selenium and theconductive layer is actually a selfsupporting metal drum. In the mostfamiliar of the electrofax processes. the photoconductive layer is acoating of zinc oxide and resin and the support'is a sheet of conductivepaper. often comprising a simple paper substrate with a thin metal foildisposed between the photoconductive coating and the substrate.

The electrophotographic film of the copending application Ser. No.378.180 is an improvement over the two electrostatic members mentionedas well as others known thus far for many reasons. Among these reasonsare greatly increased charge acceptance and high gain. rendering theelectrostatic film of said copending application Ser. No. 378.180extremely fast. In fact. the film is so fast that it is comparable withconventional high speed photographic films. but it obviates many of thedisadvantages of conventional film. For details of the said film,reference may be had to the said copending application Ser. No. 378.180,but in summary the following attributes can be mentioned briefly:

It is inorganic, transparent, grainless, and when made on a thin plasticsubstrate such as Mylar is extremely flexible. It is durable, with ahard abrasion-resistant surface. It has a dark resistivity of the orderof 10 ohms per centimeter and in undoped condition will normally have aratio of dark to light resistivity of the order of IO. It exhibits nophotoconductive persistence or fatigue no matter how repeatedly used. Itcan be charged at very high rates above saturation. will discharge inlight to practically zero residual charge and thus. in view of its highdark resistivity. will provide extreme whites and blacks when toned.with an almost infinite gradation of greys between.

The basic construction of the film of said copending application Ser.No. 378.180 comprises a layer or coating of photoconductive material ofabout 3000 Angstroms thick deposited on a plastic film which has athickness of a fraction of a millimeter. there being an interveningohmic layer about 300 to 500 Angstroms thick. The preferredphotoconductive material is cadmium sulfide. sputtered by means of r.f.to form a crystalline coating as explained in said copendingapplication; and the preferred ohmic material is indium oxide which issufficiently transparent to pass the desired amount of light. Absorbanceof light by this film is from about 707: to 85%.

The cadmium sulfide coating which has the characteristics abovementioned is in a pure state. Doping' with suitable dopants such ashydrogen iodide. copper and the like can increase the gain withaccompanying variations in other characteristics.

Other materials are described in the said copending application.

To provide an appreciation of the charge acceptance of the saidelectrophotographic film. and its high gain. it is feasible to use thefilm in a shutterless camera in which the photoconductive surface of thefilm is charged while the film is simultaneously exposed to a lightpattern. When the surface'potential reaches a predetermined value at adarkened incremental area of the film. the value having been built intocircuitry that relates it to the average light flux of the pattern beingviewed by the film. the charging is discontinued and the film is toned.These latter two functions can be effected simultaneously. Thislast-mentioned circuitry in effect adjusts the sensitivity of-the filmin accordance with the light.

The film is capable of assuming a net charge. with a full range of greytones. even though the charging and exposing occur at the same time.Prior electrostatic members. so far as known. are too slow and cannotaccept charge fast enough to accomplish this.

The construction and operation of the shutterless camera are disclosedin said copending application Ser. No. 397.309.

The method and apparatus which provides for adjustable sensitivity aredisclosed in said copending applications Ser. No. 389.149 and Ser. No.389.124.

The known methods and apparatus for charging the electrostatic membersof the prior art as well as the electrophotographic film member of saidcopending application involve the use of corona generators. A fine wire.a few thousandths of an inch in diameter. is stretched over thephotoconductive surface of the electrostatic member. being usually quiteclose. and a high voltage power supply is connected between the wire andthe conductive layer of the electrostatic member. Sometimes there isaseries of wires side by side and sometimes there is a grid between thewire or wires and the photoconductive surface. The high voltage at thewire produces a corona which ionizes the air in the vicinity of the wireand the ions move towards the coating to charge it. The charge may bepositive or negative depending upon the type of material. Selenium isusually charged positively and the cadmium sulfide of the saidelectrophotographic film is charged negatively. Many other kinds ofelectrostatic members are also charged negatively.

The charge, say for example negative comprises electrons which arelocated at or just below the surface of the coating. But for theshutterless type of camera mentioned above. the charging takes place incomplete darkness. In the case of prior electrostatic members. theircharge acceptance is so slow and the voltage to which they must becharged is so high (while still producing a 'much lower field strengththan the electrophotographic film of the copending application chargedto less than one tenth the normal surface voltage of selenium, forexample) that a shutterless camera is out of the question. The chargingmust occur in complete darkness in order to achieve a reasonably chargedphotoconductive coating.

Once charged the film is exposed to a light pattern and the impingingphotons will cause the photoconductive surface to discharge selectivelyand proportionally to' the amount of light. if any, which reaches therespective increments of area. The discharge. in the case of anegatively charged coating. represents the electrons moving toward theohmic member and combining with holes during such movement. When theexposure is completed. the light pattern is cut offQthe photoconductivesurface once more placed in darkness and the discharging is stopped at acertain point. The'film now carries a latent image in the form ofapattern of charge. Thereafter, the increments discharge in "accordancewith the dark decay characteristics of the electrostatic member orelectrophotographic film member. Electrical anisotropy of thephotoconductive coating maintains the differences in charge exhibited bythe respective increments thereof. Toning is accomplished as soon afterthe completion of exposure as possible and carried on for a time whichis normally chosen to give a good visible image. Such time may beadjusted in accordance with the value of surface potential reached.

After toning. the toned image may be transferred to another member orfixed on the electrostatic or electrophotographic film member itself.

As mentioned above, prior commercial electrostatic members havephotoconductive coatings which are very slow; they accept charge at avery slow rate and they discharge slowly in light and hence requirebright light patterns to produce any reasonable gradation. They do nothave large dark resistivities and hence they do not retain charge evenin darkness for a considerable time without loss. Improvements in thesecharacteristics have been proposed in the literature but so far asknown, very little if any of the improved coatings have beencommercialized because of many practical problems.

I have discovered that the corona which is produced by the ordinarycorona producing'mean s, comprising a fine wire or wires maintained at ahigh potential (of'the order of kilovolts) besides ionizingthe air inits vicinity, produces substantial, emission inthe ultra violet region.This radiationjhaving high energ'y,wilI effect any film that readilyresponds to ultraviolet 'r adiation' 'lhave found that ordinary silverhalide film canbe'readily "ex- 4 posed by such radiation. and the saidelectrophotographic film of the copending invention also respondsreadily to such ultra violet radiation, being panchromatic. r

In the caseof the prior electrostatic members which are in popular use.the extreme slowness of charge acceptance and the small gain and speedof the photoconductive layers or coatings thereof signified that thecharacteristics of the members were gross. In short, the members couldnot be used with the speed and flexibility of conventional photographicfilm, could not have the photographic quality of such photographic filmand hence such gross characteristics masked or were not critical enoughto be affected by ultra violet radiation during charging in darkness. Ifthere was any appreciable effect. so far as I am aware, this has notheretofore been detected. Either there has been a sufficient net chargeremaining after the charging period to give an acceptable image of theknown quality of xerography or electrofax; or the charge acceptance andlight decay characteristic are so slow that the ultra violet emissionsdont' substantially discharge the charge being applied to make anyappreciable difference in later exposure;

or both.

In the case of the electrophotographic film of the said copendingapplication Ser. No. 378,180 the characteristics which are detailed area substantial improvement over the prior art. Such improvement has been.for a very short time to give the excellent results described.

It will be appreciated from the above that if the ultra violet radiationcan be lessened to a substantial degree or even eliminated entirely, theelectrophotographic film will'exhibit characteristics vastly improvedover those which it was believed to have had. A lower corona voltage canbe used to charge the film; the charge will be accepted faster and reacha higher surface potential for any given corona producing voltage; thephotoconductive surface will exhibit greater sensitivity; it will toneeasier and faster. The entire process of charge, expose and tone can bematerially speeded up. Some improvement would be achieved in almost anyelectrostatic member or plate that has some sensitivity to ultraviolet'radiation. According to the invention, a method and means areprovided for decreasing if not wholly preventing ultra violet emissionfrom affecting the photoconductive coating of the electrophotographicfilm in the course of charging the same. In this manner I achieve vastimprovements in the characteristics of said electrophotographic film andcan increase its utility.

The environment in which the invention is used preferably is apparatusin which the charging of the photoconductive coating takes place incomplete darkness although use in a shutterless camera where chargingand exposure occur simultaneously is not excluded from the scope of saidinvention.

SUMMARY OF THE INVENTION Apparatus is provided in which there are meansfor disposing an'electrophotographic film member in darking. Chargingmeans are provided of such construction as to eliminate or substantiallydecrease the ultra violet radiation which reaches the photoconductivecoating such that there is a substantial net charge remaining on thecoating when the charging means are disabled. The charging means maytake the form of shielded corona producing means which have provisionfor blocking the paths of ultra violet emission while permitting theions produced to reach the said photoconductive surface. Such means mayalso take the form of a high speed. high potential spark gap whichproduces ionization persisting for a substantial length of time afterthe arc has decayed so that the thus-persisting ions can settle onto thephotoconductive coating and charge the same.

The method of the invention comprises charging the photoconductivecoating in such a manner as to substantially decrease or eliminate ultraviolet radiation from affecting the charge remaining on such surface.

The method and apparatus may also be used in cases where the charging isdone while exposing the electrophotographic member.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing thesteps of the method of the invention;

FIG. 2 is a similar block diagram of one variation of the invention;

FIG. 3 is a similar block diagram of another variation of the invention;

FIG. 4 is a diagrammatic view showing a form of the apparatus of theinvention using a single corona wire;

FIG. 5 is a diagrammatic sectional view through a corona wire showingone manner of blocking the ultra violet radiation from the bottomthereof;

FIG. 6 is a view similar to that of FIG. 4 but showing the use ofmultiple corona wires;

FIG. 7 is a view similar to that of FIG. 4 but showing another form ofthe invention;

FIG. 8 is a diagrammatic view showing a form of the apparatus of theinvention using a high speed spark gap and a bias device to move thecharged ions toward the electrophotographic film member;

FIG. 9 is a chart used to explain the apparatus of FIG.

FIG. 10 is a diagrammatic view of still another form of the apparatus ofthe invention; and

FIG. 11 is a diagrammatic view ofa form of the apparatus in which theshielded corona wire is physically moved across the area of theelectrophotographic film member.

DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the invention, theimprovements represented thereby are concerned with charging thephotoconductive surface or coating of an electrophotographic plate orfilm member preferably in darkness without the discharging effects ofultra violet radiation normally generated by known ionizing devices. Inthis manner the maximum of charge is applied to the coating in a minimumof time.

Considering first FIG. 1, the blocks there shown represent the basiccomponents of apparatus for recording electrostatic images on a suitablemember. The basic apparatus is designated by the reference numeral andis shown to comprise four blocks 22, 24, 26 and 28 which represent thesteps or apparatus to perform the steps in their order of use from leftto right. The usual method and apparatus as known would comprise thesesame blocks but for the construction and operation of the first.According to the prior art, this block 22 which is marked CHARGE WITHOUTULTRA VIOLET" in FIG. 1 would merely comprise a step and apparatus tocharge the electrophotographic member irrespective of whether it wasexposed to ultra violet radiation during charging. So far as known, allprior apparatus and methods of necessity resulted in the exposure of thephotoconductive coating of the electrostatic or electrophotographic filmmembers to ultra violet radiation during the charging period. Thus.although not known to the user. when the film was ready to be exposed itwas already at least partially discharged.

As seen in FIG. 1, the block 22 comprises a step in which some techniqueand/or apparatus is used by reason of which the ultra violet radiationis substantially decreased or eliminated from the ionized gas (normallyair) that is applied to the electrophotographic film member. Thus thecharged film member is exposed as indicated by the block 24 in anyconventional manner or as taught in copending applications. toned insome manner as indicated by the block 26 and thereafter furtherprocessed.

In any given apparatus, the processing after toning may take placewithin the apparatus or outside of the apparatus. Such processing maycomprise transferring the toned image and re-using theelectrophotographic film; or it may comprise fixing the toner directlyonto the film or other electrostatic member; or it may comprisephotographing the toned image or electronically reading, storing. etc.said image. The block representing any and all of these processes isdesignated 28.

The apparatus or series of steps designated 10 and representing the mostbasic form of the invention could utilize any ofa number of forms ofapparatus and modifications of the process. In FIGS. 2 and 3 twovariations are diagrammatically illustrated. FIG. 2 represents apparatusor a process 30 in which the blocks designated 24, 26 and 28 may beconsidered the same as or substantially the same as those similarlydesignated in FIGS. 1 and 3. The two blocks 32 and 34 are marked PRODUCECORONA" and SHIELD FROM UV respectively. Both blocks are shown connectedto the block 36 which is marked CHARGE IN THE DARK". All three blocks32, 34 and 36 are the equivalent of the single block 22 of FIG. I.

What is intended to be inferred from the manner of setting up thediagram with the blocks 32 and 34 both leading to the same block 36 isthat these two steps are performed simultaneously, either by some kindof fixed apparatus or by some function produced by dynamic apparatus.Such function may be effected automatically or even manually in someinstances.

Further to provide explanation in connection with FIG. 2, reference maybe had to FIG. 4 which illustrates a relatively simple form of theapparatus of the invention. Omitted from the view are components whichenable the performance of the exposing, toning or processing since thevery heart of the invention lies in the method and apparatus forachieving the most complete and efficient charge on theelectrophotographic film.

The view illustrates an electrophotographic film member 38 which ismounted in an enclosed light-free chamber, symbolically designated bythe reference character 40 along with the means 22 for producing thedesired kind of charge. This latter means include a fine corona wire 42,a. high voltage power supply 44 and leads 46 and 48 for connecting thehigh voltage supply 44 between the corona wire 42 and the ohmic layer 50of the electrophotographic film 38. The photoconductive coating 52 whichis to receive the charge faces toward the wire 42 and the substrate 54faces away from the wire. The entire apparatus 42. 44, 46 and 48comprise the means 32 for producing corona..

When the power is applied. the wire 42 will generate corona around itssurface which ionizes the air in the immediate vicinity. In knownapparatus. the charge is permitted to settle onto the photoconductivesurface 52 of the electrostatic member 38, whether of the prior art orof the copending application without any effort being made to excludeultra violet radiation. Since it has been determined that a substantialamount of such radiation is produced by corona. the charging ofth'e'photoconductive coating 52 is simultaneously accom panied by adischarging of the same so that when the power is cut off and the coronaceases, what isleft on the coating is a net charge substantially lessthan would and extent of the arc of the shield 34 are chosen in view ofthe spacing from the wire 42 and the spacing of the shield and wire.from the surface 52 so that an umbra 56 is created to shade or shieldthe coating 52 from the ultra violet radiation which emanates from thewire 42. The radiation is direct while the ionized particles produced bythe wire 42 form clouds along the wire and can move or settle down uponthe surface 52 in nonrectilinear paths. Suitable bias means as explainedin connection with FIG. 8 could also be used to drive the selectedparticles to the coating 52. For example, if it is desired to charge thesurface 52 with electrons and hence negatively, a field with thenegative polarity above the wire and the positive pole at the ohmiclayer 50 would tend to drive the electrons to the surface 52. In FIG. astructure for shielding the wire 42 is shown which is less cumbersomeand more economical than that of FIG. 4. Here, instead of a physicallyindependent shield 34, the wire 58 has a coating of paint, enamel orresin on its bottom surface as shown at 60. In FIG. 4, the shield 34 canbe any material that will block ultra violet emission and could compriseordinary glass, synthetic resins or metal.

Problems arise in the use of a shielded wire. The shield acts as a plateof a capacitor and accumulates charge thus upsetting the homogeneity ofthe cloud of ions so that the charge on the coating 52 could be laiddown unevenly. Also the umbra 56 excludes ions as well as the ultraviolet radiation thus further aggravating the condition of chargenon-uniformity.

One way of attackingthis problem is to have an array of wires each withits own shield as shown in FIG. 6. Here the wires 62 have respectiveshields 64 which produce a plurality of overlapping umbrae 66 that moreeffectively exclude the ultra violet radiation but in addition providemultiple overlapping spilLover areas for the ions thus tending to laydown a more uniform charge on the photoconductive coating.

Variations of the corona producing means 32 and the shield means 34 areillustrated in FIGS. 7, l0 and II. In FIG. 7, the, wire 68 is locatedlaterally and the shield 70 is angular or arcuate and located to oneside of the wire. The umbra 74 is arranged to shade the entire coating52 and the ions will spill over onto the entire surface. An air jet canbe used to distribute the ions .uniformly. In FIG. 10 a knife edge 76with a shielding tential there is no problem of capacitive accumulationof charge.

In FIG. 11, the wire 82 and its shade or shield 84 are carried on asmall carriage 86 riding on a track 88 that enables the wire to be movedover the area of the film 38 while producing corona. Thus, the ions forcharging are laid dowri in a progressive sweep with a maximum ofuniformity. The carriage for the electrophotographic film of thecopendingapplication would be required to move at great speed inorderltotake advantage of the high charge acceptance, presenting mechanical andin ertia problems. In slower acceptance films the carriage .could bemoved mechanically or manually. It provides an additional advantagewhere it is desired to get the charging wire out of the path of thetoning apparatus.

Reverting nowto FIG. 3, the apparatus and method 90 represented by theblock diagram illustrated uses a slightly different technique foreliminating the ultra violet radiation. As seen, the first steprepresented by the block 92 is the production of ahigh speed arcindarkness. FIG. 8 shows a high voltage supply 94 connected across a pairof points 96 and 98 spaced above the film 38. These constitute a sparkgap. The are 100 is produced at'a very high voltage, say of the order of12,000 volts and lasts for a short time, say of the order of 0.5millisecond. While the are no doubt produces ultra violet emission, thisstops with extinguishment. The ions produced by breakdown of the airhave a substantially longer persistence; hence before recombining to anysubstantial degree and dissipating their charges they will settle ontothe coating'52 of the film 38 and charge such coating. The dischargeeffect of the short burst of ultra violet radiation is exceeded by thesubsequent charging effect of free ions with no ultra violet radiationpresent. An 'added feature is represented by the independentfieldestablished between the grid 102 by the direct current voltage supply104 and the ohmic layer 50' to repel the negative ions, for example'driving them toward the surface 52. v i

The chart of FIG. 8 shows at the left the voltage and duration of theare 100 represented by the ultra violet output at 106. Note that thefluxhas subsided in about half a millisecond. The curve 108 representsthe effective surface potential and, 'as will be seen, the maximumcharge is achieved in justa few milliseconds. This represents asubstantial improvementover the charge acceptance characteristic of theelectrophotographicfilm of the copending application", a large degree ofwhich represents improvement in manufacturing techniquestions, the filmmay be charged above saturation; it may be charged to potentialscontrolled by the incident light to adjust sensitivity; and it may evenbe used in the shutterless camera with modifications. Toningis effectedin darkness irrespective of the existence of a shutter.

Variations can be made without departing from the spirit or scope of theinvention as defined in the appended claims.

What it is desired to secure by Letters Patent of the United States is:

1. Apparatus for recording electrostatic images which comprises meansfor disposing an electrophotographic member at a predetermined locationin an enclosure with its photoconductive coating in position to becharged. charging means comprising an ionproducing source structured toproduce and make available to said coating ions for charging the samewithout subjecting said coating to adversely effective ultra violetradiation. means for exposing the charged coating to a light pattern andmeans for toning the coating after exposure, said ion-producing sourceincluding a corona producing knife edge member spaced from said locationwith the knife edge facing away from said location said knife edgemember including a back blade of enlarged form facing said location andserving as-ultra violet radiation shielding means for anelectrophotographic film disposed at said location.

2. The apparatus as claimed in claim 1 in which the means for exposingand the charging means are arranged to operate simultaneously upon thesame surface.

3. The apparatus as claimed in claim 1 which includes means formaintaining said enclosure in darkness while said charging means isoperating and until said coating is charged. said exposing means servingto admit said light pattern into said enclosure after said coating ischarged.

4. Apparatus for recording electrostatic images which comprises meansfor disposing an electrophotographic member at a predetermined locationin an enclosure with its photoconductive coating in position to becharged. charging means comprising an ionproducing source structured toproduce and make available to said coating ions for charging the samewithout subjecting said coating to adversely effective ultra violetradiation, means for exposing the charged coating to a light pattern andmeans for toning the coating after exposure and said ion-producing meanscomprise a spark gap spaced above said location and circuitry forproducing an arc across said gap whose duration is less than theduration of persistence of ionization produced by said gap.

5. The apparatus as claimed in claim 4 in which includes means formaintaining said enclosure in darkness while said charging means isoperating and until said coating is charged. said exposing means servingto admit said light pattern into said enclosure after said coating ischarged.

6. ln electrostatic recording apparatus which includes an enclosure.means for mounting an electrographic film member at a predeterminedlocation in said enclosure. means for charging the surface of saidmember in darkness. means for exposing said surface to a light patternfrom the exterior of said enclosure and means for toning said surface.the invention comprising: means to prevent ultra violet radiationproduced by said charging means from adversely affecting the surfacecharge, said charging means comprising a spark gap spaced from saidsurface and said means to prevent ultra violet radiation produced bysaid charging means from adversely affecting the surface chargecomprising circuitry for arcing said gap at a speed which willextinguish the arc in substantial time before the dissipation of chargeproduced during arcing.

7. The invention as claimed in claim 6 and including bias means fordriving selected polarity ions to said surface.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. i3,880,514-

DATED April 29, 1975 INVENTORiS) I MANFRED R. KUEHNLE it is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 2, line 22 change "absorbance" to -transmittance-.

Signed and Scaled this second Day Of March 1976 [SEAL] A ttest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner ofParentsand Trademarks UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIONPATENT NO. 3,880,514

DATED April 29, 1975 |NVENT0R(5) 1 MANFRED R. KUEI-INLE It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 2, line 22 change "absorbance" to -transmittance.

Signed and Sealed this second Day Of March 1976 [SEAL] A lies I:

RUTH C. MASON C. MARSHALLDANN Arresting Officer 4 Commissioner ojPatenlsand Trademarks

1. Apparatus for recording electrostatic images which comprises meansfor disposing an electrophotographic member at a predetermined locationin an enclosure with its photoconductive coating in position to becharged, charging means comprising an ion-producing source structured toproduce and make available to said coating ions for charging the samewithout subjecting said coating to adversely effective ultra violetradiation, means for exposing the charged coating to a light pattern andmeans for toning the coating after exposure, said ion-producing sourceincluding a corona producing knife edge member spaced from said locationwith the knife edge facing away from said location, said knife edgemember including a back blade of enlarged form facing said location andserving as ultra violet radiation shielding means for anelectrophotographic film disposed at said location.
 2. The apparatus asclaimed in claim 1 in which the means for exposing and the chargingmeans are arranged to operate simultaneously upon the same surface. 3.The apparatus as claimed in claim 1 which includes means for maintainingsaid enclosure in darkness while said charging means is operating anduntil said coating is charged, said exposing means serving to admit saidlight pattern into said enclosure after said coating is charged. 4.Apparatus for recording electrostatic images which comprises means fordisposing an electrophotographic member at a predetermined location inan enclosure with its photoconductive coating in position to be charged,charging means comprising an ion-producing source structured to produceand make available to said coating ions for charging the same withoutsubjecting said coating to adversely effective ultra violet radiation,means for exposing the charged coating to a light pattern and means fortoning the coating after exposure and said ion-producing means comprisea spark gap spaced above said location and circuitry for producing anarc across said gap whose duration is less than the duration ofpersistence of ionization produced by said gap.
 5. The apparatus asclaimed in claim 4 in which includes means for maintaining saidenclosure in darkness while said charging means is operating and untilsaid coating is charged, said exposing means serving to admit said lightpattern into said enclosure after said coating is charged.
 6. Inelectrostatic recording apparatus which includes an enclosure, means formounting an electrographic film member at a predetermined location insaid enclosure, means for charging the surface of said member indarkness, means for exposing said surface to a light pattern from theexterior of said enclosure and means for toning said surface, theinvention comprising: means to prevent ultra violet radiation producedby said charging means from adversely affecting the surface charge, saidcharging means comprising a spark gap spaced from said surface and saidmeans to prevent ultra violet radiation produced by said charging meansfrom adversely affecting the surface charge comprising circuitry forarcing said gap at a speed which will extinguish the arc in substantialtime before the dissipation of charge produced during arcing.
 7. Theinvention as claimed in claim 6 and including bias means for drivingselected polarity ions to said surface.